Communication apparatus and communication method

ABSTRACT

A communication system includes a synchronizing signal generator that generates a synchronizing signal based on a timing of an alternating waveform in a power line, a data communicating circuit that performs the data communication, and a communication controller that controls to acquire a transmitting right utilizing a timing of the synchronizing signal and to control the communication circuit in accordance with whether or not the communication apparatus acquires the transmitting right.

This is a divisional application of application Ser. No. 11/745,364filed on May 7, 2007 (pending) which is a continuation of Ser. No.11/319,200 fi led on Dec. 28, 2005, which is based on and claimspriority of Japanese Application No. 2005-000163 filed on Jan. 4, 2005,the entire contents of each of which are expressly incorporated byreference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to power line communication(PLC) systems and methods for data communications over a powerdistribution system, and more particularly, to a device for facilitatingcommunications through power lines and a method of using the same.

2. Related Art

In general, when a terminal (for example, a computer terminal) performswired data communication in a home, office or factory environment, agreat deal of preparatory engineering work must be performed before acommunication system including the terminal is able to begin operations.This is because the communication system needs to install connectors andcables as transmission lines to appropriate positions.

However, with respect to power line communications, the preparatoryengineering work in such environments is reduced in comparison withother communication technologies, because almost all of suchenvironments already have in place many commercial power supply lineslocated in virtually every nook and cranny, while using a commercialpower supply, for example, alternating current 100V (50 Hz/60 Hz) inJapan or 120V in the U.S. More particularly, in the case of PLC, it willbe possible to establish a data communication line by just connecting acommunication apparatus plug to an outlet of the commercial powersupply.

JP2000-165304A describes an example of PLC technology utilizing a powerline as a data communication line.

In Japan, the frequency band from 2 MHz to 30 MHz is planned to beopened to PLC. At present, many companies are in the process of researchand development of PLC technology. However, at this time, there is noPLC standard in Japan, and each company has different specifications forPLC communications relating to protocol, modulating method, andfrequency band.

In view of the above, there is high possibility, during actual use, ofmixing different PLC communication methods in a same environment. Forexample, assuming that people who live in an apartment or condominiumcomplex use PLC apparatuses therein, they may use differentcommunication apparatuses made by different manufacturers. In suchsituation, these different communication apparatuses may besimultaneously connected to a common power line.

In such situation, each communication apparatus may not demodulatesignals from the other apparatuses that use different types of PLCcommunication methods, and may recognize these signals as noise. Becauseeach apparatus may not recognize the existence of the others on thecommon power line, signals output from different communicationapparatuses may collide with each other. Under these conditions, it maybecome almost impossible to effect a communication. That is, it maybecome almost impossible for these different PLC apparatuses to coexiston a common power line. In order to facilitate such coexistence, thesedifferent apparatuses would need to undergo significant changes to theircircuits and controllers.

On the other hand, a plurality of the same kind of PLC apparatuses areable to communicate with each other using a common power line becausethe signal multiplexing is performed based on time divisionmultiplexing.

SUMMARY

Some embodiment examples described herein address the above-mentionedproblem.

According to an embodiment example, the communication apparatusaccording to the invention comprises a synchronizing signal generatorthat generates a synchronizing signal based on a timing of analternating waveform in a power line, a data communicating circuit thatperforms the data communication, and a communication controller thatcontrols to acquire a transmitting right utilizing a timing of thesynchronizing signal and to control the communication circuit inaccordance with whether or not the communication apparatus acquires thetransmitting right.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a block diagram illustrating a communication apparatus;

FIG. 2 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 3 is a graph illustrating an example of a frequency characteristicof a transmission line using a power line;

FIG. 4 is a graph illustrating an example of a noise frequencycharacteristic of a wall outlet;

FIG. 5 is a block diagram illustrating an example of a communicationcontroller;

FIG. 6 is a wave-shape diagram illustrating an example of a signalformat outputted from a communication controller;

FIG. 7 is a diagram illustrating an example of a signal spectrum ofcontrol signals outputted from a communication controller;

FIG. 8 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 9 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 10 is a block diagram illustrating an example of a system connecteda plurality of communication apparatuses to a common transmission linein an apartment complex;

FIG. 11 is a flow chart illustrating an example of an operation forresolving a hidden apparatus problem;

FIG. 12 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 13 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 14 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 15 is a timing chart illustrating an example of an operation of aplurality of communication apparatuses;

FIG. 16 is a block diagram illustrating an example of a system connecteda plurality of communication apparatuses to a common transmission line;

FIG. 17 is a circuit block diagram illustrating a communicationapparatus shown in FIG. 1.

DETAILED DESCRIPTION OF VARIOUS EMBODIMENT EXAMPLES

Several embodiment examples will be described below with reference toFIGS. 1 and 17.

As shown in FIG. 1, a communication apparatus 100 is electricallyconnected to a transmission line 200. In this embodiment example, thecommunication apparatus operates as a modem, and communicates with acommunication terminal (not shown) such as a computer. In particular,the communication apparatus 100 may be a personal computer, a homeinformation appliance, an Internet appliance, or a digital networkappliance, or other such devices.

A power line installed in a home, an office or a factory, for example,rubber-insulated cable, is used as transmission line 200. The power linesupplies electricity of a commercial power supply, for example,Alternating Current 100V (50 Hz/60 Hz) in Japan, to each electricapparatuses. The power line may be able to utilize unused frequency bandfor data communication.

In addition, the commercial power supply is not required to bealternating current 100V (50 Hz/60 Hz) but each country has an originalstandard such as alternating current 120V (60 Hz) in the U.S. andalternating current 110/220V (50 Hz) in China.

Furthermore, when a communication apparatus 100 is installed in anapartment or a condominium complex, as shown in FIG. 16, manycommunication apparatuses 100 connect to the transmission line 200.Referring to FIG. 16, for example, a plurality of the communicationapparatuses 100A1, 100A2, 100B1, 100B2, 100C1, and 100C2 connect to thepower line 200. A pair of the communication apparatuses 100A1 and 100A2,a pair of the communication apparatuses 100B1 and 100B2, and a pair ofthe communication apparatuses 100C1 and 100C2 use communication method“A”, communication method “B”, and communication method “C”,respectively. Therefore, each of the communication apparatuses 100A1 and100A2 is the same type of the communication apparatus 100A. Each of thecommunication apparatuses 100B1 and 100B2 is the same type of theapparatus 100B. Each of the communication apparatuses 100C1 and 100C2 isthe same type of the apparatus 100C.

However, the communication types A, B and C among the communicationapparatuses 100A, 100B, and 100C are different from each other. Thedifference/differences among those three types of communicationapparatuses 100A, 100B, and 100C is/are at least one of communicationprotocol, modulation method of data signal, symbol rate of the datasignals, and so on.

Referring to FIGS. 1 and 17, a technology will be described, whichallows a plurality types of communication apparatuses to coexist on acommon transmission line 200. Hereinafter, it is assumed that there arethree communication apparatus 100A, 100B and 100C on the transmissionline 200. Each of the communication apparatuses 100A, 100B, and 100C mayhave a data communication circuit 110, a communication controller 120,an AC cycle detector 130, and a switching circuit 140 in common.

For illustrative purposes, hereinafter, a structure of the communicationapparatus 100A will be described in detail.

Communication apparatus 100A further comprises a circuit module 150 anda switching power source 160. The switching power source 160 suppliesseveral kinds of power voltages, for example +1.2V, +3.3V and +12V, tothe circuit module 150. The circuit module 150 comprises a coupler 170,a band pass filter 171, an ADC IC 176, a memory 177 and an Ethernet PHY(Physical layer) IC 174 in addition to the data communication circuit110, the communication controller 120, the AC cycle detector 130 and theswitching circuit 140

The data communication circuit 110 is an electric/electronic circuitthat performs signal processing including general control andmodulation/demodulation for the data communication as a typical modem.The data communication circuit 110 modulates a data signal or datasignals (hereinafter data signals) outputted from a terminal such as apersonal computer (not shown) to provide modulated signals, and outputsthe modulated signals as transmitted data signals. Furthermore, the datacommunication circuit 110 demodulates data signals inputted through thetransmission line 200 to provide demodulated signals, outputs thedemodulated signals as received data signals to a communication terminalsuch as a personal computer. In addition, the data communication circuit110 outputs predetermined communication request signals in advance ofthe data communication in order to confirm the condition of thetransmission line 200 including whether or not the transmission line 200is ready for the data communication.

The data communication circuit 110 comprises a main IC which comprises aCPU (central processing unit) 111, a PLC/MAC block (power linecommunication/media access control layer block) 112 and a PLC/PHY block(power line communication/physical layer block) 113. The CPU 111comprises a 32 bits RISC (reduced instruction set computer) processor.The PLC/MAC block 112 manages MAC layer of received and transmittedsignals. The PLC/PHY block 113 manages PHY layer of the received andtransmitted signals.

The switching circuit 140 is located between the data communicationcircuit 110 and the transmission line 200, and has a plurality ofswitches, which control to pass the transmitted data signals and thereceived data signals. In other words, the plurality of switches controlto switch the data communication function. The switching circuit 140comprises analog front end (AFE) IC 141, a low pass filter 142, a bandpass filter 143 and a driver IC 144. The AFE IC 141 comprises manydevices such as an analog/digital (A/D) converter 141 a, a D/A converter141 b, filters and a VGA (variable gain amplifier) 141 c, and is aninterface between the data communication circuit 110 and thetransmission line 200. The switching circuit 140 controls to pass thetransmitted data signals and/or the received data signals by switchingthese elements in the AFE IC 141.

Furthermore, the switching circuit 140 may comprise a switch, which canbe controlled to switch by an external control signal, like an analogswitch. In that case, the AFE mentioned before may be incorporated inthe data communication circuit 110. It will be recognized by thoseskilled in the art that many alternative kinds of switches can be usedas the switching circuit 140 if the switches can switch the datacommunication function.

The AC cycle detector 130 produces synchronizing signals, which is usedsuch that a plurality types of the communication apparatuses 100A, 100B,and 100C control in a common timing. The AC cycle detector 130 comprisesa diode bridge 131, registers 132 and 133, a DC (direct-current) powersupply 134 and a comparator 135. The diode bridge 131 connects to theregister 132. The register 132 connects to the register 133 in series.Both the registers 132 and 133 connect to a terminal of the comparator135 in parallel. The DC power supply 134 connects to another terminal ofthe comparator 135. Practically, as shown in FIG. 1, the AC cycledetector 130 detects points at the intersection of X-axis with the 50 Hzor 60 Hz·AC voltage sine-waveform (AC) of the commercial power sourcesupplied to the transmission line 200 (zero crossing points), producessynchronizing signals (SS) with reference to the zero crossing points,and outputs the SS. Each SS may be, for example, a rectangular waveincluding a plurality of pulses synchronizing to the zero crossingpoint. Therefore, the SS may start from the zero crossing point or mayhave a certain offset from the zero crossing point.

The communication controller 120 performs a control necessary to coexistwith the other communication apparatuses 100B and 100C, synchronizing tothe timing of the SS outputted from the AC cycle detector 130. That isto say, the communication controller 120 controls to acquire a rightthat the communication apparatus 100 uses the transmission line 200 inaccordance with communication request signals outputted from the datacommunication circuit 110. Furthermore, the communication controller 120outputs control signals as transmitted control signals to thetransmission line 200 in order to negotiate with other communicationapparatuses 100B and 100C with the right to use the transmission line200 (hereinafter, the “transmitting right”), and receives controlsignals via the transmission line 200 as received control signals. Inaddition, the controller controls the switching circuit 140 inaccordance with whether or not the communication apparatus 100A acquiresthe transmitting right, in other words, whether or not it is a timeperiod when the communication apparatus 100A can use the frequency bandof the transmission line 200.

The communication controller 120 controls to switch the switchingcircuit 140 during the time period when the communication apparatus 100can not use the frequency band on the transmission line 200. During thistime, therefore, the data communication circuit 110 disconnects to thetransmission line 200. This configuration makes it possible to prevent aplurality of different type signals outputted from a plurality ofdifferent types communication apparatuses from colliding with each otheron the transmission line 200 because, during this time, only thecommunication apparatus 100A can exclusively use the frequency band ofthe transmission line 200. Therefore, each manufacturer can select anappropriate communication protocol, an appropriate modulation method, anappropriate symbol rate, and so on in accordance with its design conceptwithout considering the collision with the other communicationapparatuses connected to the transmission line. Further, its existingcommunication circuit can be used as the data communication circuit 110without making a significant change. Moreover, at least two of thesefunctions of the data communication circuit 110, the communicationcontroller 120, the AC cycle detector 130, and the switching circuit maybe integrated into an integrated circuit.

The coupler 170 comprises a coil-type transformer 171, and couplingcondensers 172 and 173. The power source connector 180 connects to theAC cycle detector 130, the coupler 170 and the switching power source160. The coupler 170 connects to the communication controller 120 andthe switching circuit 140. The switching circuit 140 connects to thedata communication circuit 110 and RJ45 plug-in phone jack 190 via theEthernet PHY IC 174.

As shown in FIG. 2, in this embodiment example, the frequency band onthe transmission line 200 is divided into a plurality of bands such as acommercial power source band 11, a control signal band 12, and datasignal band 13. For example, the frequency band assigned to thecommercial power band is from 50 Hz to 2 MHz, the frequency bandassigned to the control signal band is from 2 MHz to 3 MHz, and thefrequency band assigned to the data signal band is from 3 MHz to 30 MHz.

The control signal band 12 is exclusively used for the negotiation toacquire the transmitting right. In other words, the control signals forthe negotiation are transmitted and received via the control signal band12. The transmitted control signal and the received control signal shownin FIG. 1 are assigned to the control signal band 12.

The data signal band 13 is exclusively used for the actual datacommunication signals. Various data signals are transmitted and receivedthrough the data signal band 13. The transmitted signal (data) and thereceived signal (data) shown in FIG. 1 are assigned to the data signalband 13.

As shown in FIGS. 3 and 4, signals transmitted in the frequency bandfrom 2 MHz to 3 MHz tend to attenuate greater than signals transmittedin the other frequency band, and tend to have more noise than signalstransmitted in the other frequency band. Although it is desirable to usefrequency band as broad as possible in order to perform fasttransmission, this frequency band (2-3 MHz) does not contribute much tothe fast transmission because the signal-to-noise ratio (S/N) of thisfrequency band is relatively low. Therefore, assigning this frequencyband to the control signal band 12 makes it possible to inhibit thetransmission speed through the transmission line 200 from lowering.

As shown in FIG. 5, the communication controller 120 comprises acontroller 121, signal generator 122, a D/A converter 123, a low passfilter (LPF) 124, a band pass filter (BPF) 125, an AGC circuit 126, anA/D converter 127, and a fast Fourier transform (FFT) circuit 128.

The controller 121 is a digital circuit, which controls the entirecommunication apparatus 100A in accordance with the communicationrequest signal, synchronizing the timing of the synchronizing signalsinputted from the AC cycle detector 130.

The signal generator 122 generates a waveform pattern of the controlsignal necessary to perform negotiation with the other communicationapparatuses 100B and/or 100C connected to the transmission line 200 inaccordance with an instruction of the controller 121. This controlsignal is a multi-carrier signal such as orthogonal frequency divisionmultiplexing (OFDM) and spread spectrum. Practically, the control signalutilizing OFDM, which has a signal spectrum as shown in FIG. 7, isproduced as shown in FIG. 6.

The D/A converter 123 converts digital OFDM signals outputted from thesignal generator 122 into analog signals.

The LPF 124 allow the analog signals with the frequency of the controlsignal band 12 to pass therethrough, and prevent the analog signal withthe other frequency from passing therethrough. Again, the frequency bandof the control signal band 12 is 2-3 MHz. In addition, the LPF 124 canbe replaced with a band pass filter.

The BPF 125 allows analog signals with the frequency of the controlsignal band 12, which are inputted from the transmission line 200, topass therethrough, and output the passed analog signals to the AGCcircuit 126.

The AGC circuit 126 automatically controls gain of passed analogsignals, and amplifies the analog signals such that the passed analogsignals from the BPF 125 can keep a specified level if the passed analogsignal attenuates.

The A/D converter 127 converts the analog signals inputted from the AGCcircuit 126 into digital signals.

The FFT circuit 128 performs predetermined FFT to the digital signalsinputted from the A/D converter 127, converts multi-carrier signalsemerging in time domain into signals in frequency domain. Here, the FFTcircuit performs FFT at 128 points. The number of the points is notlimited to 128.

The controller 121 examines the signals outputted from the FFT circuit128, and confirms whether or not a carrier relevant to a signal sent bythe communication apparatus 100B or 100C as a OFDM control signal(coexistence signal) exists in the signals outputted from the FFTcircuit 128.

Next, several controls performed by the communication controller 120,which are necessary to a plurality types of the communicationapparatuses 100A, 100B, and 100C so as to coexist on the commontransmission line 200, will be described.

As the AC waveform of the commercial power source on the transmissionline 200 is used as a common signal in a plurality of the communicationapparatuses 100A, 100B, and 100C, each switching circuit 140 of thecommunication apparatuses 100A, 100B, and 100C is controlled withsynchronizing to the AC waveform, in other words, with synchronizing tothe synchronizing signals outputted from the AC cycle detector 130.Specifically, as shown in FIG. 2, one cycle (60 Hz:16.67 milisec/50Hz:20 milisec) of the AC waveform sets as control cycle, and thecommunication apparatuses 100A, 100B, and 100C are repeatedly controlledevery one control cycle.

Specifically, the control in control cycles T2, T3, and T4 for acquiringthe transmitting right for the data signal frequency band 13 areperformed in control cycles T1, T2, and T3 of the control frequency band12, respectively.

As shown in FIG. 8, each of control cycles T1, T2, and T3 is dividedinto two periods, specifically, a first half period of the control cyclein the AC voltage waveform (the period from t1 to t2) and a second halfof the control cycle in the AC voltage waveform (the period from t2 tot3). The first half period is used for detecting a carrier. Here, thefirst half period is set as a period for performing carrier sensemultiple access with collision avoidance (CSMA/CA), in other words, aperiod for carrier detection. The second half period is set as a periodfor notice of using, in other words, a notice period. That is, withsynchronizing to the SS, the CSMA/CA period and the notice period isset.

In the CSMA/CA period, each of communication apparatuses 100A, 100B, and100C performs CSMA/CA on the basis of a predetermined back-off-rule. Inother words, one of communication apparatuses 100A, 100B, and 100C sendsthe coexist signal transmitted to the control signal frequency band 12after the one of the communication apparatuses 100A, 100B, and 100Cconfirms whether the transmission line 200 is not used for apredetermined consecutive time or more by any of the other communicationapparatuses 100A, 100B, and 100C. The predetermined consecutive time isa combination of the “waiting time” and the “minimum time.” For example,the minimum time is at least more than one symbol length. If the onesymbol length is 100 μsec, the minimum time may be more than 100 μsec,for example, 200 μsec. In this case, the random waiting time is aroundseveral tens to hundreds of μsec. Basically, the one of thecommunication apparatuses 100A, 100B, and 100C that successfullytransmits the coexist signal in the CSMA/CA period acquires thetransmitting right to exclusively use the data signal frequency band 13of the transmission line 200.

Furthermore, any of several alternative kinds of signals may be used asthe coexist signal provided these signals can discriminate carrierexistence in the control signal frequency band 12. Here, OFDM signalsare used as the coexist signal. Multi-tone signals, which have 100 μssymbol length and 56 waves therein, may be used as actual OFDM signals.

On the other hand, the notice period in the control period is dividedinto a plurality of equally spaced parts, for example 8 parts or 16parts. Each of the equally spaced parts constitutes a notice slot.Therefore, each notice period has 8 or 16 notice slot therein. In FIG.9, the notice period from t2 to t3 is divided into 8 notice slots. It isassumed here there are 8 different types of communication methods A, B,C, D, E, F, G, and H, each of which has a different protocol, adifferent modulation method, and/or a different symbol rate. The noticeslot from t21 to t22 allots to the communication method A, the noticeslot from t22 to t23 allots to the communication method B, the noticeslot from t23 to t24 allots to the communication method C, the noticeslot from t24 to t25 allots to the communication method D, the noticeslot from t25 to t26 allots to the communication method E, the noticeslot from t26 to t27 allots to the communication method F, the noticeslot from t27 to t28 allots to the communication method G, and thenotice slot from t28 to t29 allots to the communication method H. Inpractice, these different communication methods can be distinguishedfrom manufacturers of the communication apparatuses 100 or the datacommunication circuits 110.

The communication controller 120 in the communication apparatus 100 thatacquires the transmitting right in the CSMA/CA period in one of thecontrol period transmits the coexist signal to the transmission line 200at a timing of its slot allotted to its communication method in thenotice period in the same control period. In addition, each of thecommunication controllers 120 in each of communication apparatuses 100monitors conditions of all slots in the notice period, and confirmswhether each of the other communication apparatuses 100 transmits thecoexist signal.

In this example shown in FIG. 9, because the communication apparatus100B that uses the communication method B acquires the transmittingright, the communication apparatus 100B transmits the coexist signal atthe timing of the notice slot from t22 to t23. The other communicationapparatuses, for example, 100A, 100C, 100D, 100E, 100F, 100G, and 100H,which belong to communication methods A, C, D, E, F, G and H,respectively, recognize that the communication apparatus 100B that usesthe communication method B acquires the transmitting right by monitoringthe notice slot from t22 to t23.

Generally speaking, there is a possibility to collide a plurality ofsignals with each other if only the CSMA/CA is performed to control aplurality of the communication apparatuses 100. In this case, aplurality of the communication apparatuses 100, each of which has adifferent communication method, may acquire the transmitting right in asame CSMA/CA period. The communication apparatuses 100 that acquire thetransmitting right transmit a plurality of the coexist signals therefromto a plurality of the notice slots in a same notice period. This meansthat a plurality of signals will come into collision to each other inthe next control period. Therefore, the collision should be avoided.Here, all of the communication apparatuses 100 that acquire thetransmitting right monitor all notice slots. When the communicationapparatuses 100 that acquire the transmitting right detect other coexistsignal/signals in the same notice period, that is to say, each of thecommunication apparatuses 100 that acquire the transmitting right findsthe coexist signal/signals in other notice slot/slots, the communicationapparatuses 100 that acquire the transmitting right renounce thetransmitting right for the next period to avoid the collision, asexplained in detail in the example below. In this case, none ofcommunication apparatuses 100 transmits data signal in the next datasignal frequency band in the next control period.

When the other communication apparatuses 100 that acquire thetransmitting right renounce the transmitting right under the samesituation mentioned before, a communication apparatus 100 that acquiredthe last transmitting right in the last control period will successivelyacquire the transmitting right. In practice, in a case that thecommunication apparatus 100 that acquired the transmitting right in thelast control period has data signals in the next control period, thecommunication apparatus 100 that acquired the transmitting right in thelast control period monitors the notice period of next control period.When the communication apparatus 100 detects that at least two of othercommunication apparatuses 100 send the coexist signal, the communicationapparatus 100 that acquired the transmitting right in the last controlperiod will regard itself as the communication apparatus 100 thatacquires the transmitting right in the next control period, and willoccupy the data signal frequency band 13 in the next control period.

An operation above-mentioned will be described, referring to FIG. 2.

In FIG. 2, as a result of a CSMA/CA control in a control period T1, acommunication apparatus 100A that uses a communication method A acquiresthe transmitting right of a control period T2 next to the control periodT1. Further, as a result of the CSMA/CA control in the control periodT2, a communication apparatus 100B that uses a communication method Bacquires the transmitting right of a control period T3 next to thecontrol period T2.

In addition, as a result of the CSMA/CA control in the control periodT3, both the communication apparatus 100B and a communication apparatus100C that uses a communication method C may acquire the transmittingright of a control period T4 next to the control period T3. Then,however, both the communication apparatus 100B and the communicationapparatus 100C recognize by monitoring the other slots in the samenotice period that signals from both communication apparatuses 100B and100C will collide if each of communication apparatus 100A and 100Ccontinue to get into communication. Therefore, both communicationapparatus 100B and 100C renounce the transmitting right of a controlperiod T4. After both communication apparatuses 100B and 100C renouncethe transmission right, the communication apparatus B that acquired thelatest transmitting right successively acquires the transmitting rightof the data signal frequency band 13 in the control period T4.

Furthermore, as a result of CSMA/CA control and monitoring the noticeperiod in a control period, when the communication apparatus 100 thatacquired the latest transmitting right recognizes that no communicationapparatuses 100 acquire the next transmitting right, the communicationapparatus 100 that acquired the latest transmitting right successivelyacquires the next transmitting right. In other words, the communicationcontroller 120 of the communication apparatus 100 that acquired thelatest transmitting right monitors whether or not the control signal isproduced in each of the slots assigned to each of the communicationmethods. When the communication controller 120 of the communicationapparatus 100 that acquired the latest transmitting right finds noproduced signals in each slot during monitoring, the communicationcontroller 120 acquires the next transmitting right. This configurationmakes it possible to efficiently use the frequency band because one ofcommunication apparatuses 100 will always get the transmitting right.

As an alternative of the above-mentioned embodiment example, it may alsobe possible to control that none of the communication apparatuses 100transmits data signal in the next data signal frequency band in the nextcontrol period.

Next, an operation in a condition that there is at least one hiddenterminal that is hidden from other terminals will be described.Generally, there is a possibility that one or some of the communicationapparatuses 100 is/are hidden from other communication apparatuses 100in an environment that a plurality of communication apparatuses 100coexist on the transmission line 200. That is to say, in a case that thetransmission line 200 like a power line is used, communicationconditions of communication apparatuses 100, each of which connects tothe transmission line 200, dynamically fluctuates in response to lineconnection status and/or operation status of a variety of electricdevices. The fluctuation of the communication conditions may cause theattenuation of signals or a high noise level. Therefore, sometimes atleast one of communication apparatuses 100 connected to the sametransmission line 200 may not be observed by the other communicationapparatuses 100.

In an example shown in FIG. 10, it is supposed that both the home of Mr.X and the home of Mr. Y are in a same housing complex, and communicationsystems in the X's home and the Y's home, which are different from eachother, share the transmission line 200 (not shown in FIG. 10) in common.In FIG. 10, the left oval shows the X's home, and the right oval showsthe Y's home. There are a same kind of three communication apparatusesA1, A2, and A3 in the X's home, and there are a same kind of threecommunication apparatuses B1, B2, and B3 in the Y's home. Therefore, allof the communication apparatuses A1, A2, A3, B1, B2, and B3 connect tothe transmission line 200 in common.

Moreover, in the example shown in FIG. 10, the communication apparatusesA1, A2, and A3 can communicate with each other, and the communicationapparatuses B1, B2, and B3 can communicate with each other. However,because of many reasons such as communication distance between bothhomes and degradation of frequency characteristic caused by connectionsof many communication apparatuses to the transmission line 200, thecommunication apparatus A1 can be observed by all of the communicationapparatuses B1, B2, and B3, and the communication apparatus B1 can beobserved by all of the communication apparatuses A1, A2, and A3;however, the other combinations among communication apparatuses A1, A2,A3, B1, B2, and B3 can not observe each other.

Therefore, in the environment shown in FIG. 10, when either thecommunication apparatus A1 or B1 acquires the transmitting right, thenthere is no problem with communication because all of the communicationapparatuses can observe the communication apparatuses A1 and B1.However, for example, when the communication apparatus B2 acquires thetransmitting right, the communication apparatuses A2 and A3 do notrecognize that communication apparatus B2 connects on the transmissionline 200 because coexistence signal transmitted from the communicationapparatus B2 in a notice period may not be observed by the communicationapparatuses A2 and A3, and either the communication apparatus A2 or A3also acquires the transmitting right in the next control period in spiteof the fact that the communication apparatus B2 acquires thetransmitting right. Therefore, signals from the communication apparatusB2 collide with signals from either the communication apparatuses A2 orA3. A control to avoid the collision due to the hidden terminal will bedescribed hereinafter.

In the control shown in FIG. 11 to avoid the collision due to the hiddenterminal, each of the communication controllers 120 independentlymonitors frequency of collision of a plurality of signals. When thefrequency is high, each of the communication controllers 120 regards asbeing at least one hidden terminal on the transmission line 200, andperforms a specific control to deal with the existence of the hiddenterminal(s). Specifically, as an example, each step of the apparatus A1in FIG. 11 will be explained hereinafter.

In step “S11”, the communication controller 120 in the communicationapparatus A1 identifies whether or not the communication apparatus A1acquires the transmitting right of the data signal frequency band innext control period. When the communication apparatus A1 identifies toacquire the transmitting right in the S11, then the communicationcontroller 120 goes through the following step “S12” to add “1” to avalue of a transmitting right counter (the number of acquiring thetransmitting right).

In the next step “S13”, the communication controller 120 identifieswhether a plurality of the communication apparatuses A1, A2, A3, and B1(B2 and B3 are hidden from A1) transmit coexistence signals in aplurality of slots in the same notice period, that is, whether aplurality of coexistence signals are outputted in overlapping conditionsin the same notice period. When the communication controller 120identifies the coexistence signals in a plurality of slots, thecommunication controller 120 regards the conditions as occurring thecollision, proceeds to the following step “S14”, and adds “1” to a valueof a collision counter (the number of occurring the collision).

In the next step “S15”, the communication controller 120 calculatescollision frequency (the value of the collision counter/the value of thetransmitting right counter), and makes a comparison between thecollision frequency and a predetermined threshold (for example, 0.9).The collision frequency tends to be relatively low when no hiddencommunication apparatus exists on the transmission line 200. On theother hand, the frequency of the collision tends to be relatively highwhen at least one hidden communication apparatus exists on thetransmission line 200.

As a result of the comparison, when the collision frequency is lowerthan the threshold, the communication controller 120 regards thiscondition as indicative of no hidden communication apparatus on thetransmission line 200, proceeds to a step “S17”, and gets into normaltransmission. Meanwhile, as a result of the comparison, when thecollision frequency is higher than the threshold, the communicationcontroller 120 regards this conditions as indicative of at least onehidden communication apparatus on the transmission line 200, proceeds toa step “S16”, and stops transmitting signals for a certain amount oftime period (the so-called back-off time period). Specifically, thecommunication controller 120 stops transmitting a coexistence signal inthe CSMA/CA period for a predetermined time period (e.g., 1 to 10seconds). This control makes it possible to suppress occurrences of thecollision in case that at least one hidden communication apparatus is onthe transmission line 200.

Furthermore, in step S17, the back-off time period for which thecommunication apparatus A1 stops transmitting signals is not necessaryto be a constant, but may be changeable. For example, a back-off timeperiod of a communication apparatus in which the collision frequency ishigher than the threshold may be set longer than those of the othercommunication apparatuses. That is, if a default back-off time of acommunication apparatus, whose collision frequency exceeds thethreshold, is the same as a default back-off time of other communicationapparatuses, the back-off time of the communication apparatus, whosecollision frequency exceeds the threshold, may change to a longerback-off time. For example, if the default back-off time is set at 1second, the back-off time of the communication apparatus, whosecollision frequency exceeds the threshold, may change to 2 seconds, asone example. Furthermore, the communication controller 120 can returnthe back-off time period to the original period when predeterminedconditions, for example, after a lapse of a predetermined time and atthe time when the collision frequency becomes lower than the thresholdor other value, is met. For example, the back-off time may change from 2seconds to 1 second.

Another control shown in FIG. 12 also provides a measure to deal withthe hidden terminal problem. In addition, it is possible to perform thecontrol shown in FIG. 11 and another control shown in FIG. 12simultaneously, and it is also possible to perform either the controlshown in FIG. 11 or another control shown in FIG. 12.

The communication apparatuses A1, A2, and A3 belong to the samecommunication system A. When the communication apparatus A1 identifiesin a slot in the notice period that one of the communication apparatusesA2 and A3, in other words, a communication apparatus Ax belonging to thesame communication system A, acquires the transmitting right, thecommunication apparatus A1 transmits the coexistence signal to thetransmission line 200 using the same slot as the communication apparatusAx.

In an example shown in FIG. 12, it is assumed that the communicationapparatus B3 acquires the transmitting right in the same environmentshown in FIG. 10. Therefore, the communication apparatus B3 transmitsthe coexistence signal to the transmission line 200 using B-slots thatis the time period from t22 to t23 assigned to the communication systemB in the notice period. As explained previously referring to FIG. 10,the coexistence signal transmitted from the communication apparatus B3is detected by the communication apparatuses B1, B2, and A1 because thecommunication apparatus B3 is visible from the communication apparatusB1, B2, and A1.

In this case, both the communication apparatuses B1 and B2 transmit thecoexistence signals to the transmission line 200 when both thecommunication apparatuses B1 and B2 detect the coexistence signaltransmitted from the communication apparatus B3. Specifically, inresponse to detecting the coexistence signal from the communicationapparatus B3 in the first half of the B-slot, both the communicationapparatuses B1 and B2 also transmit the coexistence signals to thetransmission line 200 in the last half of the B-slot. Consequently, thecoexistence signal in the last half of the B-slot transmitted from B1 isdetected by the communication apparatus A2, and A3. Therefore, even in asituation that the communication apparatus B3 is hidden from thecommunication apparatuses A2 and A3, the communication apparatuses A2and A3 can identify that one communication apparatus belonging toanother communication system B acquires the transmitting right. Thiscontrol makes it possible to prevent the communication apparatusesbelonging to either of two communication systems from suffering acollision.

Next, another control will be described. For example, when a terminalsuch as a personal computer accesses to a network like the Internet, itis usual to connect the terminal to a provider using a transmission linelike metal line or an optical fiber line. Furthermore, it is alsopossible to connect between users and the provider using a power linethat supplies a commercial power source. Here, a communication methodusing the power line in a user's home is called an “in-home-systemcommunication method” (hereinafter “in-home-system”). Each of the othercommunication methods is called an “access-system communication method”(hereinafter “access-system”). Specifically, the access-system includescommunication system using a power line connecting between a power poleand each home, or a power line in an office or a factory.

In the case of connecting between users and the provider using a powerline, both at least one communication apparatus of the in-home-systemand at least one communication apparatus of the access-system connect tothe common power line connect to the common power line. Therefore, acollision between signals from the access-system and signals from thein-home-system should be also avoided in this case. In addition,regarding the access-system, it is usual that there is only one kind ofaccess-system communication method on a power line if several kinds ofcommunication apparatuses, which are made by different makers, do notconnect to the power line. However, it is also possible that, forexample, a communication system provided by a communication company andanother communication system provided by an electric power company shareone power line, that is, there may be a plurality of the access-systemson the same power line.

In the above-mentioned cases, basically it is possible to prevent acollision between a plurality kinds of signals by using theafore-mentioned communication apparatus 100 in the in-home-system. In anexample shown in FIG. 13, communication systems A and B show differentkinds of in-home-system communication apparatuses 100A and 100B,respectively. A communication system C shows an access-systemcommunication apparatus 100C.

In this example, time slots in the notice period mentioned previously,each of which is independent of each other, are assigned to thecommunication systems A, B, and C. Therefore, each of the communicationsystems A, B, and C can ensure a frequency band (data signal frequencyband 13) by performing CSMA/CA control under equal conditions.

In this example, by performing a CSMA/CA control in a CSMA/CA period ina control period T1, the communication system A, which is anin-home-system, acquires a transmitting right for the data signalfrequency band 13 in a control period T2 next to the control period T1.By performing a CSMA/CA control in a control period T2, thecommunication system B acquires a transmitting right for the data signalfrequency band 13 in a control period T3. By performing a CSMA/CAcontrol in a control period T3, the communication system C, which is anaccess-system, acquires a transmitting right for the data signalfrequency band 13 in a control period T4.

All of the communication systems including both access-systems andin-home-systems are assigned different identification data,respectively. The control for acquiring the transmitting right isperformed based on the identification data. Therefore, this makes itpossible to avoid a collision between signals from the in-home-systemand signals from the access-system. In addition, it may be possible toassign only one identification data to the entire access-systemcommunication system, or it is also possible to assign differentidentification data to each access-system communication system.Assigning different identification data to each access-systemcommunication system allows a plurality of access-system communicationsystems to coexist on a same transmission line. In addition, acoexistence signal comprises the identification data in this example.

A modified example will be described with reference to FIG. 14. Thelonger length of a transmission line that is used for actualcommunication, the more the high frequency signal component greatlyattenuates in the access-system. Therefore, transmission speed in theaccess-system may not improve even if the frequency band used in theaccess-system broadens. In that case, for example as shown in FIG. 14,it is preferable to divide the data signal frequency band 13 into alower portion (for example, 3 MHz to 10 MHz) and a higher portion (forexample, 10 MHz to 30 MHz) and to assign the lower portion to theaccess-system. Efficiency of the use of frequency thus may be improved.

In the example shown in FIG. 14, by performing a CSMA/CA control in aCSMA/CA period in a control period T3, the communication system Cacquires a transmitting right for the lower portion in the data signalfrequency band 13 in a control period T4 next to the control period T3.The communication system B, which acquired the transmitting right in thelast control period T3, again acquires a transmitting right for thehigher portion, which is not used by the communication system C, in thedata signal frequency band 13 in a control period T4.

In this case, the communication apparatus 100B of the communicationsystem B monitors a notice slot allotted to the communication system Cin the notice period, in other words, the communication apparatus 100Bdetects the identification data of the communication system C. Thus, thecommunication apparatus 100C recognizes whether the communication systemC acquires a transmitting right. If the communication apparatus 100Brecognizes that the communication apparatus 100C acquires thetransmitting right to the control period T4, the communication apparatus100B is operable to keep a transmitting right for only the higherportion in the control period T4.

Another modified embodiment example will be described with reference toFIG. 15. In the embodiment example shown in FIG. 15, the communicationsystem C does not perform the CSMA/CA control. Instead, thecommunication system C will acquire a transmitting right for exclusivelyusing the lower portion in the data signal frequency band 13 as needed.The communication system C will notice in the notice slot in the noticeperiod that the communication system C, which is an access-system,acquired the transmitting right.

In this example shown in FIG. 15, it is assumed that no collision occursbetween an access-system and an in-home-system. Therefore, although eachof the in-home-system A and the access-system C sends a coexistencesignal, which represents acquisition of a transmitting right, in a samenotice period, this is not a collision, and actually, both thecommunication system A and the communication system C acquire thetransmitting right in the next control period T4.

In this case, the communication apparatus 100A of the communicationsystem A only uses the higher portion in the data signal frequency band13 in the next control period T4 if the communication apparatus Adetects that the communication system C acquires the transmitting rightin the notice period.

In addition, it also may be possible that the communication apparatus100C of the communication system C acquires the transmitting rightregardless of detecting at least one of control signals sent from othercommunication apparatuses 100A and 100B, and sends a control signalrelated to the acquisition of the transmitting right in the noticeperiod assigned to the communication apparatus 100C in advance.

Assuming that communication in an apartment is made using a power line,a first user in the apartment may connect the same kinds ofcommunication apparatuses manufactured by a same maker to the powerline. However, the more the number of users utilizing power linecommunication increases, the more different kinds of communicationapparatuses may be connected to the power line. In a case that only onekind of communication apparatuses connect to a same power line, thecontrols mentioned above may not be necessary since no collision betweena plurality of signals occurs on the transmission line 200.

Therefore, another control performed in the communication apparatus 100will be described. Each communication apparatus 100A, for example,counts how many times each communication apparatus 100A or eachcommunication system A, to which each communication apparatus 100Abelongs, acquires the transmitting right (hereinafter the “acquisitionnumber”). Then the communication apparatus 100A compares the acquisitionnumber for a predetermined period with a predetermined threshold (forexample, 100 times). Or the communication apparatus 100A comparesacquisition frequency (the acquisition number/the number of transmittingcarrier signals) with a predetermined threshold (for example, 0.99). Ifthe acquisition number or the acquisition frequency is equal to orgreater than the threshold, that is, the frequency of acquiring thetransmitting right is high, the communication apparatus 100A decidesthat there is no different kind of communication apparatus 100B or 100C,or communication system B or C in the transmission line 200. In thiscase, the communication apparatus 100A fixes the condition of theswitching circuit 140 to be “on” for a certain period (for example, tenminutes or more), and acquires the transmitting right in all controlperiods. Furthermore, the communication controller 120 is also operableto stop sending the control signal. Thus, not only aforementioned datasignal frequency band 13 but also the control signal frequency band 12can be utilized for data transmission. Therefore, efficiency of the useof frequency may be improved.

In addition, as an alternative to the abovementioned control mode, it ispossible to perform another control mode described below. Thecommunication apparatus 100A counts how many times the othercommunication apparatuses 100B or 100C, or the other communicationsystem B or C, acquires the transmitting right (hereinafter the“acquisition number of other system”). Then the communication apparatus100A compares the acquisition number of other system for a predeterminedperiod with a predetermined threshold. If the acquisition number ofother system or the acquisition frequency of the other system is equalto or less than the threshold (for example, ten times or 1%), that is,frequency of acquiring the transmitting right by other system is low,the communication apparatus 100A decides that there is no different kindof communication apparatus 100B or 100C or communication system B or Cin the transmission line 200.

As time advances, a different kind of communication apparatus 100B or100C may connect to the transmission line 200. Even if the communicationapparatus 100A is under a condition that the communication apparatus100A decided that there was no different kind of communication apparatus100B or 100C, or communication system B or C in the transmission line200, and stopped sending the control signal, the communication apparatus100A decides that a different kind of communication apparatus 100B or100C is connected to the transmission line 200 when the acquisitionnumber counted by the communication apparatus 100A is not greater thanthe threshold. Then, the communication apparatus 100A changes itscontrol mode to, for example, the control mode shown in FIG. 2.

According to these embodiment examples described herein, thecommunication apparatus controls a communication timing based on asynchronizing signal generated at a specific timing of AC voltagesine-waveform of the commercial power source. Therefore, these examplesmake it possible to control a variety of timings such as signaltransmission, monitoring a timing slot or the like, appropriately. Theseexamples make it possible to prevent signals being a kind of noise frombeing transmitted to the transmission line by performing such a controlthat a communication apparatus, which does not acquire a transmittingright, turns off its transmitting function. Therefore, different kindsof signals are prevented from colliding to each other on a power line,and different kinds of communication apparatuses can coexist on a commonpower line.

In addition, although several embodiment examples are described that allcontrol a transmitting right, transmitting a control signal in thenotice period and data transmission are performed based on the righttiming of the synchronizing signal SS, transmitting a control signal inthe notice period and data transmission may be performed starting at apredetermined time after the SS is outputted. The predetermined time ispreferable to be less than a half of the AC period; for example, if thefrequency of the AC is 50 Hz, then the predetermined time is less than8.3 milliseconds, for example 3 milliseconds. In addition, thepredetermined time is not necessary to be a constant value among allcommunication apparatuses. For example, each of different kinds ofcommunication apparatuses employing different kinds of specificationsmay be set a different predetermined time.

In some cases, it may not be necessary for the communication apparatusto synchronize with the synchronizing signal SS if the communicationapparatus utilizes the synchronizing signal SS, in some way. Forexample, in a case that the synchronizing signal SS comprises arectangular wave with one pulse synchronizing with one zero crossingpoint of AC sine waveform, the communication apparatus may control thetransmitting right after a specific time based on the one pulse.

Furthermore, if the communication apparatus performs a control oftransmitting right via the power line, transmitting a control signal inthe notice period and data transmission are not necessary to beperformed via the power line. A transmission line for data transmissionmay be wired or wireless. A variety of cables, such as a LAN cable, acoaxial cable, a telephone line and a speaker line, may be used as thewired transmission line.

In addition, although the above-mentioned embodiment examples show thata data signal and a control signal are independent of each otherregarding frequency by dividing frequency band into control signalfrequency band and data signal frequency band, it is enough if the datasignal and the control signal are independent of each other. Forexample, the control signal band and the data signal band overlap eachother, and the data signal and the control signal are transmitted in atime divisional mode.

Although preferred embodiment examples have been described and disclosedfor illustrative purposes, those skilled in the art will appreciate thatvarious modifications, additions, and substitutions of these examplesare possible, without departing from the scope and spirit thereof.

This description is based on Japanese Patent Application No.2005-000163, filed on Jan. 4, 2005, the entire subject matter of whichis expressly incorporated by reference herein.

1. A communication apparatus, which performs a data communicationthrough a power line transmitting alternating current havingpredetermined frequency, and which uses a first communication method,the communication apparatus comprising: a data communication circuitthat performs the data communication; a detecting circuit that detects,within a period synchronized with the predetermined frequency, a signaltransmitted from another communication apparatus, the anothercommunication apparatus using a second communication method differentfrom the first communication method; and a controlling circuit thatcontrols the data communication circuit in accordance with whether ornot the detecting circuit detects the signal.
 2. The communicationapparatus according to claim 1, wherein the alternating current isgenerated from a commercial power source.
 3. The communication apparatusaccording to claim 1, wherein the predetermined frequency is one of 50Hz and 60 Hz.
 4. The communication apparatus according to claim 1,wherein the detecting circuit detects the signal within the periodsynchronized with a point being located an offset off from a zerocrossing point of the alternating current.
 5. The communicationapparatus according to claim 4, wherein the offset is about zero.
 6. Thecommunication apparatus according to claim 1, wherein the datacommunication circuit performs the data communication with a MHzfrequency band.
 7. The communication apparatus according to claim 6,wherein the frequency band includes from 2 MHz to 30 MHz.
 8. Thecommunication apparatus according to claim 1, wherein the signaltransmitted from the another communication apparatus is a preamble. 9.The communication apparatus according to claim 1 further comprising: aswitching circuit that switches the data communication performed by thedata communication circuit, wherein the controlling circuit controls thedata communication circuit through the switching circuit.
 10. Thecommunication apparatus according to claim 1, wherein the datacommunication circuit performs the data communication based on CSMA/CA“Carrier Sense Multiple Access with Collision Avoidance.”
 11. Thecommunication apparatus according to claim 1, wherein the datacommunication circuit performs the data communication using a datasignal, and wherein a communication method including the first and thesecond communication method includes at least one of communicationprotocol, modulation method of the data signal, symbol rate of the datasignal.
 12. A communication apparatus, which performs a datacommunication through a power line transmitting alternating currenthaving predetermined frequency, and which uses a first communicationmethod, the communication apparatus comprising: a data communicationmeans that performs the data communication; a detecting means thatdetects, within a period synchronized with the predetermined frequency,a signal transmitted from another communication apparatus, the anothercommunication apparatus using a second communication method differentfrom the first communication method; and a controlling means controlsthe data communication means in accordance with whether or not thedetecting means detects the signal.
 13. A communication method, whichperforms a data communication through a power line transmittingalternating current having predetermined frequency, and which uses afirst communication method, the communication method comprising:performing the data communication; detecting, within a periodsynchronized with the predetermined frequency, a signal transmitted fromanother communication apparatus, the another communication apparatususing a second communication method different from the firstcommunication method; and controlling the data communication inaccordance with whether or not the signal is detected.